Durability. You’re paying a lot of money and a costly investment that lasts for a short time is not worthwhile. The electric bike has more components than the common bike, adding the electric motor and the battery; more attention should be put in selection of the bike because of this. You don’t want your electric bike to turn into a regular bike in a short period.
Some power-on-demand only e-bikes can hardly be confused with, let alone categorised as, bicycles. For example, the Noped is a term used by the Ministry of Transportation of Ontario for e-bikes which do not have pedals or in which the pedals have been removed from their motorised bicycle. These are better categorised as electric mopeds or electric motorcycles.

E-bikes use rechargeable batteries and the lighter ones can travel up to 25 to 32 km/h (16 to 20 mph), depending on local laws, while the more high-powered varieties can often do in excess of 45 km/h (28 mph). In some markets, such as Germany as of 2013, they are gaining in popularity and taking some market share away from conventional bicycles,[1] while in others, such as China as of 2010, they are replacing fossil fuel-powered mopeds and small motorcycles.[2][3]

Ironically, not only would a US e-bike manufacturer need to import the raw materials for their frames, but they could still be subject to import tariffs that the Trump administration has placed on imported steel and aluminum from China. Thus, the e-bikes could end up even more expensive than just US-built e-bikes, as customers would also have to pay for the higher cost of the imported raw materials.

This 48-volt mid-motor electric mountain bike is a great value. The X-Treme Summit is packed with top-of-the-line components from Shimano, Suntour, Tektro, Samsung, Kenda, Velo, and more. With a top speed of 28 mph and tremendous torque from the mid-frame mounted motor, it conquers rough terrain and inclines like a champ. Pull power from the motor by pedal assist and throttle.

The way they work is pretty simple: The motor kicks in with extra assist when you pedal, and there are different levels of assistance. That's it. Just turn it on, pedal, and go! You can also turn the assist mode off and ride it like a regular bike. And e-bikes stop assisting at a certain speed (in the U.S., it's 20 mph or 28 mph depending on class) for safety, of course.
Above all, the Brompton is a lot of fun to ride in urban settings. Its powerful enough to breeze up hills with near zero effort, but feels nimble. As with any Brompton, you probably won't win a half-mile sprint on it, but thanks to the pedal assistance, you most certainly will get off to a flying start. The reason it stands above other electric bikes is that Brompton has worked out how to apply power assistance to your pedalling so it feels natural. It also doesn't feel so much like it's trying to fight you once you reach the maximum, 15mph assisted speed.
Because e-bikes are capable of greater speeds for longer periods of time than standard bikes, you want extra control. Wider tires provide traction and some bump absorption with little penalty. You also want strong brakes to slow you (and all that extra weight) easily. It's worth looking at the quality of the brakes and investing in bikes with better ones if you can.